1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to an AAL-2/AAL-5 processing apparatus disposed in a base station (BTS) and a base station controller (BSC).
2. Description of the Background Art
Generally, in the ATM (Asynchronous Transfer Mode) transmission method, user information is divided into packets of a predetermined size, and a header, e.g., destination information, is appended to the divided packet for thereby transmitting an ATM cell of a fixed size(53 bytes) to its destination. At this time, an user data having a low bit rate fills parts of the effective load of the ATM cell, and the remainder thereof is padded to xe2x80x9c0xe2x80x9d to be transmitted.
Therefore, in the case that the ATM transmission method is applied to a wireless network, data (sound data) of a low bit rate transmitted from a plurality of mobile terminals being provided with services from the same base station is packed with each different ATM cell, the effective load part of the ATM cell is wasted. In addition, during the transmission of small length packets packed with a single ATM cell, small length packets transmitted from other mobile terminals cannot be transmitted.
In this way, in the case that the ATM transmission method is applied to the wireless network, partially filled cells are transmitted for thereby degrading the transmission efficiency of links with respect to the network, and a predetermined time has to be waited in order to pack each data to be transmitted for thereby occurring a transmission lag with respect to the system.
AAL Type 2(AAL-2) recommended to solve this problem can reduce the time taken for packing small length user data with ATM cells and effectively use the bandwidth of the ATM network, by multiplexing small length packets transmitted from multiple users on the ATM network into a single ATM cell. That is, the function of multiplexing multiple user data of variable length or small length into a single ATM cell or decomposing the same is a basic technique of AAL-2.
In an ATM system, user information, e.g., a protocol for transmitting packet data consists of a physical layer, ATM layer, AAL layer, and upper layer. The AAL layer is a layer for reassembling packet data delivered from the upper layer into 48 bytes. The ITU-T (International Telecommunication Union-Telecommunication) recommendation defines AAL-1xcx9cAAL-5 protocols.
FIG. 1 is a view explaining a conventional AAL-2 protocol.
As illustrated therein, an AAL-2 layer is divided into SSCS (Service Specific Convergence Sublayer) and CPS (Common part Sublayer).
First, when packet data in SDU(Service Data Unit) transmitted from a mobile station through the service access point (SAP) 10 of the upper layer is inputted, the SSCS of the AAL layer appends a header and a trailer to an inputted SDU(AAL-SDU) 11 to generate a SSCS-PDU(Protocol Data Unit) 12.
In addition, the CPS appends a CPS-header to a transmitted SDU(CPS-SDU) 13 to generate a CPS-packet 14, and adds a start field to a CPS-packet payload to generate a 48-byte CPS-PDU 15. The data structure of the CPS-packet 14 and CPS-PDU 15 is illustrated in FIGS. 2 and 3.
As illustrated in FIG. 2, the CF""S-packet consists of a CPS-packet header and a CPS-packet payload. The CPS-packet header consists of a 8-bit CID (Channel Identifier) field identifying a plurality of users in a single virtual channel (hereinafter, referred to as xe2x80x98VCxe2x80x9d), 6-bit LI (Length Indicator) field indicating the size of the effective load of the CPS-packet, SSCS data, UUI field (User-to-User Indication) field indicating a CPS user and a network manager, and 5-bit HEC (Header Error Control) field for the control of an error in the CPS-packet header. At this time, because the CID field is 8 bits, a single VC can hold 256 users.
In addition, as illustrated in FIG. 3, the CPS-PDU wherein CPS-packets from the plurality of users are multiplexed consists of a start field and a CPS-PDU payload. The start field consists of an OSF (Offset Field) field, SN (Sequence Number) field, and Parity (P) field each used for identifying a CPS-packet boundary by a receiving side. In addition, the CPS-PDU payload consists of a CPS-INFO field and PAD (Padding) field indicating packet data of the users. At this time, the CPS-packets become the CPS-PDU payload, and the CPS-packets transmitted from the plurality of users are multiplexed into the CPS-PDU payload.
Afterwards, the CPS-PDU generated from the AAL-2 layer is transmitted to the ATM layer through the service access point(ATM_SAP) 16, and the ATM layer appends a 5-byte ATM header to the 48-byte CPS-PDU to thus generate an ATM cell 17 of the total 53 bytes and thereafter transmit it to its destination through the ATM network. In this manner, packet data transmitted from each mobile station is assembled into 48 bytes through the AAL-2 protocol to thus be used as the payload of the ATM cell.
In this way, in the conventional mobile communication system to which the AAL-2 protocol is adapted, a number of packet data is multiplexed into a single VC(Virtual Channel) to be transmitted. However, since only the single VC has been mentioned in the fields relating to the AAL-2 recommended in the ITU-T until now, it is not relevant to implement the AAL-2 protocol in an actual ATM network. In addition, there is no method for transmitting packet data(or cells) through Multiple Virtual Channels, that is, a plurality of virtual channels recommended as a standard yet.
Therefore, in the mobile communication system to which the AAL-2 protocol is adapted, since it is impossible to transmit packet data from a plurality of mobile stations base stations, and base station controllers to its destination through a plurality of virtual channels, there is a problem that there occur limitations upon capacity of users and transmission speed.
Meanwhile, in the communication system to which the ATM system is adapted, signals related to system management are classified into signals for allocating a CID of each user in the AAL-2 protocol and system control signals (signals for overall communication network flow control, bandwidth allocation control, and call set-up control). At this time, the signal for allocating a CID is controlled by ANP(AAL-2 Negotiation Procedures) according to the AAL-2 protocol, and the signal used as a system control signal is controlled according to the AAL-5 protocol.
Accordingly, it is an object of the present invention to provide an AAL-2/AAL-5 processing apparatus in a mobile communication system which is capable of transmitting an AAL-2 traffic through multiple virtual channels.
It is another object of the present invention to provide an AAL-2/AAL-5 processing apparatus in a mobile communication system which is capable of processing an AAL-5 signal, a system control signal, along with an AAL-2 traffic.
To achieve the above objects, there is provided an AAL-2/AAL-5 processing apparatus in a mobile communication system according to the present invention which includes: an user interface for transmitting/receiving cells by connecting to an AAL-2 user; transmission/receiving interface for transmitting/receiving cells by connecting to an ATM layer; an AAL-2 receiving unit for receiving an AAL-2 cell from the transmission/receiving interface and deassembling the same into mini cells to thereafter transmit them to each AAL-2 user; an AAL-2 transmission unit for multiplexing the AAL-2 cell inputted from the user interface into a single cell to thus transmit the same to the ATM layer; an AAL-5 processing unit for processing an AAL-5 signal transmitted from either one of the ATM layer and the AAL-2 user; and a CPU for controlling the AAL-2 receiving unit and the AAL-2 transmission unit upon receipt of the AAL-5 signal from the AAL-5 processing unit.
Additional advantages, objects and features of the invention will become more apparent from the description which follows.